Doping of semiconductor materials with conductivity-determining type dopant elements, such as n-type and p-type dopant elements, is used in a variety of applications that require modification of the electrical characteristics of the semiconductor materials. Typically, elements such as phosphorous, arsenic, or antimony are used to fabricate n-type doped semiconductor materials, while boron is used to fabricate p-type doped semiconductor materials.
In some applications such as, for example, solar cells, it is desirable to dope a semiconductor substrate with dopant-type elements of different conductivity in a pattern having very fine lines or features. FIG. 1 illustrates one type of solar cell 10. Solar cell 10 has a silicon substrate 12 having a light-receiving front side 14 and a back side 16 and is provided with a basic doping, wherein the basic doping can be of the n-type or of the p-type. The light-receiving front side 14 has a rough or textured surface that serves as a light trap, preventing absorbed light from being reflected back out of the solar cell. Metal contacts 20 of the solar cell are formed on the back side 16 of the wafer. The silicon wafer is doped at the backside relative to the metal contacts, thus forming p-n junctions 18 within the silicon substrate. Photons from light are absorbed by the light-receiving side 14 to the p-n junctions where charge carriers, i.e., electrons and holes, are separated and conducted to the metal contacts, thus generating electricity. Solar cell 10 has an advantage over other types of solar cells in that all of the metal contacts of the cell are on the back side 16. In this regard, there is no shading of the light-receiving front side 14 of the solar cell by the contacts. However, for all contacts to be formed on the back side 16, the doped regions adjacent to the contacts have to be quite narrow.
Present-day methods of doping, such as photolithography and screen printing, present significant drawbacks for forming such narrow features. For example, it is prohibitively difficult, if not impossible, to obtain very fine and/or narrow doped regions in a semiconductor substrate using screen printing. In addition, while doping of substrates in fine-lined patterns is possible with photolithography, using photolithography to form different doped regions is an expensive and time consuming process, involving multiple deposition, masking, and etching steps. In addition, both photolithography and screen printing involve contact with the semiconductor substrate. However, in applications such as solar cells, the semiconductor substrates are becoming very thin. Contact with thin substrates often results in breaking of the substrates. Moreover, because photolithography and screen printing use custom designed masks and screens, respectively, to dope the semiconductor substrate in a pattern, reconfiguration of the doping pattern is expensive because new masks or screens have to be developed.
Accordingly, it is desirable to provide methods for fabricating semiconductor devices by depositing dopants comprising conductivity-determining type dopant elements of opposite conductivity overlying a semiconductor material using non-contact printing processes and simultaneously diffusing the elements into the semiconductor material. In addition, it is desirable to provide methods for fabricating semiconductor devices by depositing a liquid dopant comprising n-type elements and a liquid dopant comprising p-type elements overlying a semiconductor material and diffusing the elements into the semiconductor material using one diffusion step. It is also desirable to provide methods for fabricating semiconductor devices with fine or thin doped features. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.